1. Field of the Invention
This invention relates to a method for making a steering wheel for use in a vehicle such as an automobile.
2. Description of the Related Arts
In general, the steering wheel comprises a metal core at the ring portion, a metal core at the spoke portion which is joined to the metal core of the ring portion, a boss, which is joined to the metal core of the spoke portion and which is fitted to the steering shaft and a coated layer made of polypropylene, polyvinyl chloride, urethane or the like which is coated along the outer periphery thereof by injection molding, RIM molding, casting or the like.
Among these metal cores for the steering wheel, the metal core at the ring portion is, in many cases, of a circular shape in transverse cross-section, which is likely to cause the offset caused by sliding which occurs at the boundary between the metal and the above coating layer during the use of the above steering wheel, with the result of which the corresponding portion can be peeled off. Consequently, in recent years, it has been suggested that the cross section of this core metal at the ring portion should be defined in a non-circular form, for example, in a rectangular or pentagonal form for the purpose of preventing the above-mentioned sliding.
In case the coating layer made of the synthetic resin is defined by injection molding along the outer periphery of the metal core at the ring portion, the metal core is placed in the mold as shown in FIG. 6. Namely, in the molding groove portions 41a and 42a of a pair of molds for injection molding, the metal core at the ring portion 45 is placed in such a way that a portion wherein the gap is increased between the molding grooves 41a and 42a and the metal core 45 is opposed to a surface along which the mold is to be opened.
However, in case the ring portion metal core 45 is disposed in this way to form the coating layer 44, the synthetic resin can flow with predominance during the injection molding into the wider space at the cavity between the above molding grooves 41a and 42a and the metal core. Consequently, the air within the cavity is collected into the coating layer 44 portion which coats an angular portion 45a of the above ring metal core 45, a portion where the resin flows most slowly to reside there to cause a bad appearance due to air hardening or a weld line at this portion of the article.